1. Field of the Invention
The present invention relates to a magneto-resistive element including a magnetization fixed layer in which magnetization is fixed in a direction, a tunnel barrier layer formed on the magnetization fixed layer, and a magnetization free layer formed on the tunnel barrier layer, and a production method thereof.
2. Description of the Related Arts
In a tunnel barrier layer formed from a non-magnetic and insulating material and sandwiched by two magnetic layers, when a current is applied approximately vertically with respect to the magnetic layers, a so-called tunnel current flows from one of the magnetic layers to the other. This phenomenon is known as the ferromagnetic tunnel effect.
This tunnel current has a conductance changing according to a relative angle of the magnetization directions of the two magnetic layers. In the aforementioned ferromagnetic tunnel effect, it is possible to theoretically calculate a reluctivity from the polarizability of magnetization of the two magnetic layers. For example, when the two magnetic layers are made from Fe, the reluctivity is estimated to be about 40%.
For this, a magneto-resistive element (hereinafter, referred to as an MR element) utilizing the aforementioned ferromagnetic tunnel effect, which is called a tunnel junction type MR element (hereinafter, referred to as a TMR element), is expected as a material for a magneto-resistive magnetic head (hereinafter, referred to as an MR head).
The MR head detects a voltage value of a current flowing in the MR element via electrodes and reads a magnetic signal recorded on a magnetic recording medium.
The aforementioned TMR element includes a tunnel barrier layer formed from a non-magnetic and insulating material and sandwiched by a magnetization fixed layer in which magnetization is fixed and a magnetization free layer in which magnetization is not fixed. A change of the magnetization direction of the magnetization free layer by an external magnetic field changes the relative angle defined by the magnetization direction of the magnetization fixed layer and the magnetization direction of the magnetization free layer. This in turn changes the conductance of the tunnel current. When the TMR element is utilized for an MR head, this conductance change is detected so as to read a magnetic signal.
In the MR head, in order to suppress the Barkhausen noise, it is important to perform a magnetic domain control so that the MR element has a single magnetic domain. As in a conventional MR head when an anisotropic magneto-resistive (AMR) element and a giant magneto-resistive (GMR) element are used as magnetism detection elements, at the both ends of the MR element, there are arranged a bias layer formed from a hard magnetic material for applying a bias magnetic field to the MR element. Thus, the MR element has a single magnetic domain.
However, when an MR head is produced using a TMR element, an electrode is arranged on both main surfaces of the TMR element and an electric current is applied approximately vertically with respect to the film surface, so as to determine a conductance of the tunnel current flowing through an insulation layer for reading a magnetic signal. Accordingly, when a bias layer is arranged at the both ends of the TMR element, it becomes impossible to maintain insulation between the magnetization free layer and the magnetization fixed layer, short-circuiting the TMR element, disabling to read a magnetic signal.
For this, in an MR head using the TMR element as a magnetism detecting element, it becomes impossible to perform a magnetic domain control by providing a bias layer at both ends of the TMR element.
The aforementioned magnetization fixed layer has a ferromagnetic layer and an anti-ferromagnetic layer. The anti-ferromagnetic layer is in exchange coupling with the ferromagnetic layer. Accordingly, in the magnetization fixed layer, magnetization is controlled. However, in the magnetization free layer, magnetization is not controlled.
It is therefore an object of the present invention to provide a magneto-resistive element capable of suppressing the Barkhausen noise to obtain a stable reproduction even when utilizing the ferromagnetic tunnel effect and a production method thereof.
In order to achieve the aforementioned object, the magneto-resistive element according to the present invention includes: a magnetization fixed layer whose magnetization is fixed in a predetermined direction, a tunnel barrier layer formed on the magnetization fixed layer, and a magnetization free layer formed on the tunnel barrier layer and whose magnetization direction freely changes. Moreover, a non-magnetic metal layer is present on the magnetization free layer and a conductive anti-ferromagnetic layer is formed on the non-magnetic metal layer.
In the magneto-resistive element having the aforementioned configuration, the magnetization free layer and the conductive anti-ferromagnetic layer are in exchange coupling via the non-magnetic metal layer. Accordingly, it is possible to control a magnetic domain without fixing the magnetization direction of the magnetization free layer.
Moreover, the magneto-resistive element production method includes a layering step for layering on a substrate, a lower shield layer, a lower gap layer, a magnetization fixed layer, a tunnel barrier layer, a non-magnetic metal layer, and a conductive anti-ferromagnetic film.
According to the magneto-resistive element production method of the present invention, it is possible to provide a magneto-resistive element in which magnetic domain control can be performed without fixing the magnetization direction in the magnetization free layer.